Lamination Process for Manufacture of Integrated Membrane-Electrode-Assemblies

ABSTRACT

A process for manufacture of integrated membrane-electrode-assemblies (MEAs), which comprise an ionomer membrane, at least one gas diffusion layer (GDL), at least one catalyst layer deposited on the GDL and/or the ionomer membrane, and at least one protective film material is disclosed. The components are assembled together by a lamination process comprising the steps of heating the components to a temperature in the range of 20 to 250° C. and laminating the materials by applying a laminating force in the range of 50 to 1300 N with a pair of rolls. The claimed lamination process is simple and inexpensive and is used for manufacture of advanced, integrated MEAs for electrochemical devices such as PEM fuel cells and DMFC.

The present invention refers to the manufacture of electrochemicaldevices such as fuel cells, batteries, electrolyzer cells orelectrochemical sensors. In more detail, the present invention providesa process for manufacturing of integrated membrane-electrode-assemblies(MEAs) for fuel cells. Such integrated MEAs comprise of a polymerelectrolyte membrane, at least one electrically conductive, porous gasdiffusion layer (“GDL”), at least one catalyst layer deposited on themembrane and/or the GDL, and additionally at least one protective filmmaterial, serving as a sealant, reinforcement or protective film layer.

Fuel cells convert fuel and oxidant directly into electric power andheat in an electrochemical reaction without the limitations of theCARNOT process. Nowadays, a significant number of fuel cell applicationsuse a solid polymer electrolyte membrane (PEM) disposed between the twocatalytic active compartments, this type of cell is usually referred toas PEM Fuel Cell (PEMFC).

The polymer electrolyte membrane fuel cell (PEMFC) and the directmethanol fuel cell (DMFC, a variation of the PEMFC, powered directly bymethanol instead of hydrogen) are suitable for use as energy convertingdevices due to their compact design, their power density and highefficiency. The technology of fuel cells is broadly described in theliterature, see for example K. Kordesch and G. Simader, “Fuel Cells andits Applications”, VCH Verlag Chemie, Weinheim (Germany) 1996.

In the following section, the technical terms and abbreviations used inthe present patent application are described in greater detail:

A membrane-electrode-assembly (“MEA”) is the central component in apolymer electrolyte membrane fuel cell (PEMFC) or DMFC stack andbasically consists of five layers: The anode GDL, the anode catalystlayer, the ionomer membrane, the cathode catalyst layer and the cathodeGDL. A MEA can be manufactured by combining a catalyst-coated membrane(CCM) with two GDLs (on the anode and the cathode side) or,alternatively, by combining an ionomer membrane with two catalyst-coatedbackings (CCBs) at the anode and the cathode side. One of the catalystlayers takes the form of an anode for the oxidation of hydrogen and thesecond layer takes the form of a cathode for the reduction of oxygen.Due to its fragile nature, the ionomer membrane and the MEA isfrequently reinforced or protected by a protective film material forbetter handling, gasketing and/or sealing.

Gas diffusion layers (“GDLs”), sometimes referred to as gas diffusionsubstrates or “backings”, are placed onto the anode and cathode layersof the CCM in order to bring the reaction media (hydrogen or methanoland air) to the catalytically active layers and, at the same time, toestablish an electrical contact. GDLs usually consist of carbon-basedsubstrates, such as carbon fiber paper or woven carbon fabric, which arehighly porous and allow the reaction media a good access to theelectrodes. In most cases, they are hydrophobic in order to remove theproduct water from the fuel cell. GDLs can be coated with a microlayerto modify their water management properties. They can be tailoredspecifically into anode-type GDLs or cathode-type GDLs, depending onwhich side they are built into a MEA. Furthermore, they can be coatedwith a catalyst layer and subsequently laminated to the ionomermembrane. These catalyst-coated GDLs are frequently referred to as“catalyst-coated backings” (abbreviated “CCBs”) or gas diffusionelectrodes (“GDEs”).

The anode and cathode catalyst layers comprise electrocatalysts, whichcatalyse the respective reaction (oxidation of hydrogen at the anode andreduction of oxygen at the cathode). The metals of the platinum group ofthe Periodic Table are preferably used as catalytically activecomponents. For the most part, supported catalysts are used, in whichthe catalytically active platinum group metals are fixed in form ofnano-sized particles to the surface of a conductive support material.The average particle size of the platinum group metal is in the range ofabout 1 to 10 nm. Carbon blacks with particle sizes of 10 to 200 nm andgood electrical conductivity have proven to be suitable as supportmaterials.

The polymer electrolyte membrane comprises proton-conducting polymermaterials. These materials are also referred to below as ionomermembranes. A tetrafluoro-ethylene-fluorovinyl-ether copolymer withsulfonic acid groups is preferably used. This material is marketed forexample by E.I. DuPont under the trade name Nafion®. However, other,especially fluorine-free ionomer materials such as sulfonated polyetherketones or aryl ketones or acid-doped polybenzimidazoles may also beused. Suitable ionomer materials are described by O. Savadogo in“Journal of New Materials for Electrochemical Systems” I, 47-66 (1998).For application in fuel cells, these membranes generally have athickness between 10 and 200 μm.

For future widespread commercialization of the PEMFC and DMFCtechnology, industrial-scale, economical production processes forcatalyst-coated membranes (CCMs) and membrane-electrode-assemblies(MEAs) are required. Such MEAs are needed for manufacturing ofcommercial quantities of stacks for mobile, stationary and portableapplications. The manufacturing processes must be economical,continuous, fast, environmentally safe and with high throughput. Theserequirements also apply to the coating and lamination processescurrently used in MEA production.

Generally, various technologies for laminating of materials areapplicable. The standard processes such as reciprocal (hydraulic) pressbonding and roller bonding are well known to the person skilled in theart.

WO 02/091511 describes the use of a double belt press for themanufacture of MEAs for PEM fuel cells. Either isobaric or isochoricbelt presses are employed for the lamination of MEA materials. Due tothe elongated processing zone, these presses allow higher productionspeeds and continuous material conveyance. Two elongated, streched steelbelts are used for pressure application. Due to the rather rigid steelbelts, these machines are unable to respond to thickness variations orto different step heights in the processed materials. Thus, GDLs and/orCCBs and frames of protective film materials cannot be laminatedtogether in one single pass. Moreover, the equipment is very expensiveand bulky. The stretching of a steel belt requires a rigid machinedesign and due to the bending stiffness of the steel belt, large drumshave to be employed to drive the belt.

WO 97/23919 discloses a continuous production process formembrane-electrode-composits. The lamination of the components can beperformed by a pair of rollers or by a press at temperatures up to 300°C. and a high pressure in the range of 10⁷ to 10¹² Pa.

WO 01/61774 teaches the manufacture of a reinforced ion exchangemembrane by use of a roll-to-roll process. A double belt press or a beltcolander is employed for pressing or rolling the materials.

EP 1 369 948 A1 discloses a process for the manufacture ofmembrane-electrode-assemblies using a catalyst-coated membrane andadhesive components.

In summary, the draw-backs of the state of the art are:

-   a) In the materials employed, an uneven height distribution is    found, namely in the gas diffusion layers (GDLs). Lamination    processes with rigid press platens or steel rollers lead to a    non-uniform distribution of the resulting laminating forces. To    ensure proper lamination in each point of the surface, rather high    pressure has to be employed. Due to this high pressure, a high    compression of the GDLs occurs, which in turn may result in a    destruction of the GDL structure. Generally, for reciprocal    (hydraulic) press bonding and for bonding with steel rollers as    described in the state of the art, it is known that the compression    of the GDLs is usually more than 10% of their original thickness.-   b) Integrated MEA materials (e.g. 7-layer MEAs as described    hereinafter) cannot be laminated. Different substrate heights due to    additional rims of protective film material cause steps in the    substrate to be laminated. In the region of the steps, non-uniform    pressure is applied and proper lamination is not possible.-   c) Insufficient control of the temperature and pressure during    lamination. Due to height differences in the material and a process    design which is unable to react to that properly, the pressure and    the temperature cannot be predicted and controlled properly. If the    temperature and/or pressure for lamination is too high, thickness    deviations and even shortings in the MEA may occur.-   d) High cost of the equipment. This refers particularly to    double-belt presses as disclosed in WO 02/091511.

It was therefore the object of the present invention to provide animproved process for manufacture of integratedmembrane-electrode-assemblies (MEAs), which avoids the disadvantages ofthe state of the art. In particular, it was an object of the inventionto provide an improved lamination process incorporating the advantagesof low pressure and tight control of the temperature/pressure profilefor substrate heating. Additionally, the process should allow theprocessing of integrated MEAs and similar products with temperature-and/or pressure-sensitive components. The process and equipment thereforshould be economical viable (i.e. of reasonable costs).

This object was achieved by the manufacturing process of claim 1 of thepresent invention. It provides a process for manufacture of anintegrated membrane-electrode-assembly (MEA) comprising an ionomermembrane, at least one gas diffusion layer (GDL), at least one catalystlayer deposited on the GDL and/or the ionomer membrane, and at least oneprotective film material, wherein the ionomer membrane, the at least onegas diffusion layer (GDL), the at least one catalyst layer and the atleast one protective film material are bonded together in a laminationprocess comprising the steps of:

-   -   (a) heating the components to a temperature in the range of 20        to 250° C.    -   (b) laminating the components by applying a laminating force        with a pair of rolls.

Preferred embodiments of the process are disclosed in subsequent,dependent claims. Optionally, the claimed process embraces an additionalcooling step (c) for cooling the laminates after heat and pressureapplication. The claimed process is used for lamination of integratedMEAs, which contain temperature- and/or pressure-sensitive componentssuch as protective film materials.

A suitable device for lamination of the integratedmembrane-electrode-assemblies (MEAs) according to the process of claim 1is depicted in FIG. 1.

A continuous transporting belt (1), comprising the lower heating platen(5) in the heating zone and optionally the lower cooling platen (6) inthe cooling zone (6, 6 a), is mounted on a bench-type rig. The laminatorcomprises a second belt (2) containing the upper heating platen (5 a) inthe heating zone (5, 5 a) and optionally a third belt (3) containing theupper cooling platen (6 a) in the cooling zone (6, 6 a). A pair of rolls(4, 4 a) is applying the pressure for lamination. The pressure to theupper roll (4 a) is supplied by a pneumatic pressure unit (7, 7 a). Theheating platens (5, 5 a) and cooling platens (6, 6 a) can be supportedby a self-adjusting construction. This is achieved by supporting theupper platens only in the center line by means of pendulum-typebearings. Generally, the device can be constructed inexpensive andsimple and can be integrated in a continuous manufacturing line ofintegrated MEAs (“reel to reel” process). The process can also beoperated in a discontinues way by use of discrete material sheets orblanks.

In a preferred embodiment, the rolls (4, 4 a) are not directly heated,since the thermal energy is supplied in the heating zone (5, 5 a). Inthis preferred embodiment, at least one of the rolls (4, 4 a) of thelamination device is coated with a soft, elastomeric material. Whenusing rubber or silicone-coated rolls, MEAs containing steps and/orheight deviations due to protective film frames can be properlyprocessed. At any process speed, the rolls will easily response to suchheight variations, even when in the machine direction of the materials.At least one of the two rolls (4, 4 a) should be pneumatically loaded(i.e. pressurized) with the suitable laminating force.

In a further preferred embodiment, a PTFE (Teflon®) belt is used for thetransporting belt (1). Instead of PTFE, similar materials such asreinforced glass fiber belts or silicone-coated fiber glass belts may beused. There is no need for stretching the belts, and the driving drums(i.e. the coated rollers) can be small in diameter due to the lowbending stiffness of the belts. Thus, the machine may be constructedonly for a fraction of the cost needed for a double belt press.

The process provides sufficient dwell time in the heating zone (5, 5 a)to generate an uniform temperature distribution. It is of greatimportance that the ionomer membrane has reached its glass transitionpoint (T_(g)) when the GDL or CCB components are laminated to theionomer membrane to form the MEA. Unfortunately, the membrane becomesductile and fluid when heated to the T_(g) and when under pressure. Ifthe lamination process is not properly controlled in temperature andpressure, thickness deviations and even shortings may occur in thelaminated assembly.

The temperature in the heating zone is in range of 20 to 250° C.,preferably in the range of 100 to 200° C. Typically, the heating zone(5, 5 a) has longitudinal dimension of less than 1 m and the (optional)cooling zone has dimensions of less than 0.8 m. The temperature in thecooling zone is adjusted in the range of 10 to 50° C. Typically, thebelt speed in the heating zone is in the range of 1 to 500 m/h,preferably in the range of 50 to 200 m/h. Similar figures apply for theoptional cooling zone.

The employed materials, especially the gas diffusion layers (GDLs) arerelatively non-uniform in their thickness. In general, it has been foundthat working with rolls means averageing the product thickness over thebandwidth, whereas reciprocal (i.e. hydraulic) press bonding meansaverageing over a two-dimensional area, which results in an uneven forcedistribution in the lamination process.

Surprisingly, it was found that in the claimed process the gas diffusionlayers (GDLs) suffer a compression of less than 10%, typically as low as5% of their original thickness. For comparison, it is known fromreciprocal press bonding or conventional roller bonding with steelrollers, that the compression of the GDLs is about more than twice asmuch (i.e. >10% of their original thickness).

At least one of the two rolls (4, 4 a) of the laminator is pressurizedwith a suitable pneumatic pressure unit (7, 7 a). The pressure to theupper roll (4 a) is adjusted by a pressure indication controller (PIC).The air inlet pressure is used as a measure for the laminating forceapplied to the upper roll (4 a). Generally, the air inlet pressure is inthe range of 0.25 to 6 bar, preferably in the range of 1 to 3.5 bar. Thelaminating force applied to the upper roll (4 a) can be calculated to bein the range of 50 to 1300 N, preferably in the range of 200 to 750 N.

The diameter of the rolls (4, 4 a) is in the range of 50 to 100 mm,their length is in the range of 100 to 800 mm.

In summary, the claimed lamination process surpasses the prior state ofthe art. The assembly to be laminated is brought under pressure for theshortest possible time in the nip of the rollers, but still the separateheating zone provides for an even temperature distribution within thematerial. In contrast to the double belt press, pressure is only appliedby a single pair of rolls, preferably rolls (4, 4 a). No areal pressureis applied. The gas diffusion layers (GDLs) and/or catalyst-coated GDLs(CCBs) laminated to the ionomer membrane according to the claimedprocess retain their original structure. This is due to a very lowcompression of less than 10% , preferably of less than 6% of theiroriginal thickness. As a consequence, their performance regarding watermanagement is much better compared to the products made by conventionallamination processes. Superior integrated MEA products are manufacturedby the claimed process.

Suitable lamination devices are commercially available and can bepurchased at Vaporetta Geraetebau (Koeln, Germany) or AdamsInternational Technologies (Ball Ground, Ga. USA), Glenro Inc.(Paterson, N.Y. USA) or Meyer Maschinenbau (Roetz, Germany).

The integrated MEA products may enclose 4-, 5-, 6-, 7-layer MEAs,multilayer MEAs, MEAs with additional gasketing layers, MEAs withintegrated gasket frames and the like.

In FIG. 2, an example for an integrated MEA product is shown (in thiscase a 7-layer MEA). The individual components are depicted in aschematic drawing in the pre-assembled state. The 7-layer MEA comprisesof an ionomer membrane (A), two catalyst layers (B, C), either depositedon the GDL or onto the membrane, two electrically conductive, porous gasdiffusion layers (GDLs) (D, E), and two frames of protective filmmaterial (F, G). Variations of this basic assembly are possible in orderto arrive at MEAs with lower or higher layer count or different layersequences. In a very simple version, an integrated 4-layer MEA comprisesof an ionomer membrane (A), at least one gas diffusion layer (D), atleast one catalyst layer deposited on the GDL and/or the ionomermembrane (B) and at least one protective film material (F).

Various types of commercial available GDLs as well as other materialscan be used for the manufacture of the integratedmembrane-electrode-assembly (MEA). As base materials for GDLs (D, E),woven carbon cloth, non-woven carbon fiber layers or carbon fiber papersmay be used. The GDLs may be hydrophobically treated or not. They maycomprise of additional microlayers and catalyst layers, if necessary.

The protective film material (F, G) comprise of thermoplastic polymersselected from the group of polyethylenes, polypropylenes,polytetrafluorethylenes, PVDF, polyesters, polyamides, polyimides andpolyurethanes, and/or elastomeric materials selected from the group ofsilicones, silicone elastomeres, EPDM, fluoro-elastomers,perfluoro-elastomers, chloropren-elastomes, fluorosilicone-elastomers,and/or duroplastic polymers selected from the group of epoxy resins,phenolic resins and cyano-acrylates.

For positioning the components prior to their assembly, varioustechnologies known to those skilled in the art can be employed. Thehandling and positioning of the components can be made sheetwise orcontinuously or even in a mixture of both, automatically or in manualoperation. In assembly of the integrated MEAs, a part of the GDL surfacemay overlap with the protective film materials. The area of theoverlapping zone depends on the size of the MEA product and theoperating conditions. Preferably, the overlapping area is in the rangeof 0.1-20% of the total area of the GDL, most preferably it is in therange of 0.2-10% of the total area of the GDL.

Generally, the lamination process of the present invention as well asthe lamination device can be operated separate or it can be integratedinto a continuous manufacturing line for integrated MEAs.

EXAMPLES

The following examples describe the invention in more detail. Theseexamples are presented to aid in an understanding of the presentinvention and are not intended to, and should not be construed to, limitthe scope of the invention in any way.

Example 1

A 7-layer MEA as depicted in FIG. 2 is manufactured. An ionomermembrane, (Nafion® NR 117, DuPont) is coated with two catalyst layers toproduce a CCM according to known processes (ref. to EP 1 037 295). TheCCM has an active area of 50 cm² (7×7 cm) and a total area of 100 cm²(10×10 cm). In a second step, two porous gas diffusion layers (Sigracet30 BC, dimensions 7.5×7.5 cm; SGL, Meitingen) are positioned on the topand on the back side of the CCM. Two frames of protective film material(Vestamelt®, Degussa, Duesseldorf), each with outer dimensions of 10×10cm and inner dimensions of 7×7 cm and a thickness of 150 μm areprepared, the first frame is positioned on the top and the second frameon the bottom of this assembly. Parts of the GDL surface are overlappingwith the protective film material. The area of the overlapping zonedepends on the size of the product and the operating conditions.Preferably, the overlapping area is in the range of 0.1-20% of the totalarea of the GDL, most preferably it is in the range of 0.2-10% of thetotal area of the GDL. Then, the materials are passed through thelamination device as described in the present invention, applying thefollowing operating conditions: Temperature: 175° C. Pressure (air inletpressure): 3.5 bar Belt speed: 150 m/h Diameter of rolls (4, 4a): 80 mmLength of rolls (4, 4a): 500 mm Laminating force applied to roll (4a):750 NAfter a single pass, the integrated 7-layer MEA product is completed.

Example 2

An ionomer membrane (thickness 25 μm) is coated with two catalyst layersto form a CCM by processes known to those skilled in the art. A frame ofprotective film material made of Platilon® (Epurex, Germany) with athickness of 50 μm is positioned on the top side the CCM, and then theGDL (Sigracet 21 BC; SGL, Meitingen) is positioned on the frame in sucha way, that parts of the GDL overlap with the protective film material.The area of the overlapping zone depends on the size of the product andthe operating conditions. Preferably, the overlapping area is in therange of 0.1-20% of the size of the GDL, most preferably it is in therange of 0.2-15% of the size of the GDL. A second GDL is then positionedon the back side of the membrane onto a second frame of protective filmmaterial in the same way. Parts of the GDL overlap with the protectivefilm material. Then, the stacked materials are passed through thelamination device. In this example, the laminating conditions are:Temperature: 135° C. Pressure (air inlet pressure): 2.2 bar Belt speed:100 m/h Laminating force applied to roll (4a): 480 NAfter a single pass, the final integrated 7-layer MEA is completed. Thecompression of the gas diffusion layers (GDLs) during lamination isabout 2.7% of their original thickness.

Example 3

An ionomer membrane, in this example Nafion® NR 112 (DuPont) isinterposed between two electrodes (i.e. catalyst-coated backings,CCB's). The electrodes each consist of a GDL (Sigracet 30 BC; SGL,Meitingen), coated with an anode (respectively cathode) catalyst layeraccording to methods well known to those skilled in the art. Two framesof protective film material are prepared from a film of Vestamelt®(Degussa, Duesseldorf) having a thickness of 190 μm. The first frame ispositioned on top of the membrane, and then the first CCB is positionedonto said frame in a manner that the frame exactly stretches out fromthe boundaries of the CCB. The second CCB is positioned on the back sideof the ionomer membrane and a second protective film frame is addedthereto. The overlapping areas between the protective film frames andthe electrodes are formed during impregnation of the CCBs in thelamination process The area of the said impregnation zone depends on theframe thickness and the laminating conditions. Preferably, the said areais in the range of 0.1-20% of the size of the GDL, most preferably it isin the range of 0.2-15% of the size of the GDL. The materials are passedthrough the laminating device. In this example, the laminatingconditions are: Temperature: 175° C. Air inlet pressure: 3.5 bar Beltspeed: 80 m/h Laminating force applied to roll (4a): 750 NAfter a single pass, the MEA product is completed and can be used forthe manufacture of PEMFC or DMFC single cells and stacks. Thecompression of the catalyst-coated GDLs (CCBs) during lamination isabout 3.2% of their original thickness.

1. Process for manufacture of an integrated membrane-electrode-assembly(MEA) comprising an ionomer membrane, at least one gas diffusion layer(GDL), at least one catalyst layer deposited on the GDL and/or theionomer membrane, and at least one protective film material, wherein theionomer membrane, the at least one gas diffusion layer (GDL), the atleast one catalyst layer and the at least one protective film materialare bonded together in a lamination process comprising the steps of: (a)heating the components to a temperature in the range of 20 to 250° C.(b) laminating the components by applying a laminating force with a pairof rolls (4, 4 a).
 2. The process according to claim 1, wherein thelaminating force is in the range of 50 to 1300 N, preferably in therange of 200 to 750 N.
 3. The process according to claim 1, wherein theair inlet pressure for pressurizing at least one of the rolls (4, 4 a)is in the range of 0.25 to 6 bar, preferably in the range of 1 to 3.5bar.
 4. The process according to claim 1, wherein the at least one gasdiffusion layer undergoes a compression of less than 10% of its originalthickness during lamination.
 5. The process according to claim 1,wherein the belt speed in the heating zone is in the range of 1 to 500m/h, preferably in the range of 50 to 200 m/h.
 6. The process accordingto claim 1, further comprising a cooling step (c) after the heating step(a) and the laminating step (b).
 7. The process according to claim 1,wherein the rolls (4, 4 a) are not directly heated.
 8. The processaccording to claim 1, wherein at least one of the rolls (4, 4 a) iscoated with soft elastomeric material of the group comprising ofrubbers, natural rubbers, silicone rubbers, polyurethane elastomers andthe like.
 9. The process according to claim 1, wherein the ionomermembrane comprises of fluorinated ionomer materials such astetrafluoroethylene-fluorovinyl-ether co-polymers with sulfonic acidgroups or fluorine-free ionmer materials such as sulfonatedpolyetherketones, polyarylketones or acid-doped polybenzimidazoles andthe like.
 10. The process according to claim 1, wherein the gasdiffusion layer (GDL) comprises of woven carbon cloth, non-woven carbonfiber layers or carbon fiber papers and is optionally hydrophobicallytreated and/or coated with a microlayer and/or coated with a catalystlayer.
 11. The process according to claim 1, wherein the catalyst layercomprises of precious metals from the platinum metals group of thePeriodic Table, such as, e.g., platinum, ruthenium, gold, silver,palladium and/or mixtures or combinations thereof.
 12. The processaccording to claim 1, wherein the protective film material comprises ofthermoplastic polymers selected from the group consisting ofpolyethylenes, polypropylenes, polytetrafluorethylenes, PVDF,polyesters, polyamides, polyimides and polyurethanes.
 13. The processaccording to claim 1, wherein the protective film material comprises ofelastomeric materials selected from the group consisting of silicones,silicone elastomeres, EPDM, fluoro-elastomers, perfluoro-elastomers,chloropren-elastomers and fluorosilicone-elastomers.
 14. The processaccording to claim 1, wherein the protective film material comprises ofduroplastic polymers selected from the group consisting of epoxy resins,phenolic resins and cyano-acrylates.
 15. Use of the process according toclaim 1 for manufacture of integrated MEAs for electrochemical devicessuch as polymer electrolyte membrane fuel cells (PEMFC), direct-methanolfuel cells (DMFC), batteries, electrolyzer cells or electrochemicalsensors.
 16. Continuous manufacturing process for integrated MEAs,comprising the lamination process according to claim 1.